Young and older adults reported their daily perceived control and subjective well-being over nine weeks. Trait conscientiousness (C) was positively associated with mean daily life satisfaction and positive affect, greater fluctuation in perceived control (state-level C), and also modified the daily associations between control and negative affect. The negative covariation between perceived control and negative affect was stronger for people lower in trait C. Age cohort predicted daily affective well-being but did not interact with C. Findings are discussed in the context of proposals for a multilevel structural and process approach to personality and its application to different life phases.